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Which RAM Speed with CPU FSB

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  • RAM
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Last response: in Memory
January 6, 2009 9:39:43 AM

I'm buiding a new conf but I have I question about Frequency, as I didn't practice for a long time.

My mother board have RAM speed up to 2000
The CPU have FSB 1333
My RAM is 1600.

Is it better to downgrade the RAM to 1333, to match the CPU FSB, or 1600 wil provide better performance ? (About the same price)


More about : ram speed cpu fsb

January 6, 2009 11:04:02 AM

Hi craneduitre

I don't know much about this, but I was just reading this article, it might be of help:

Quote: Although synchronizing the memory speed and the FSB speed is best it is OK to use memory that is faster then the FSB of your processor provided that the motherboard supports it.

Good luck!
January 6, 2009 11:07:49 AM

I went with 1333 RAM on my latest build, as personally I believe the 1600Mhz stuff should only be bought of you want to overclock.

1333Mhz RAM will aslo run at lower timings.
Related resources
January 6, 2009 11:17:43 AM

Just by DDR2-800 which runs at FSB-1600.

Don't even consider DDR2-667.
January 6, 2009 11:22:25 AM

ok thanks.

I forgot to say that its DDR3 (zenmaster)
January 6, 2009 3:48:41 PM


Hi there. I read the article from your link (kind of old but OK to understand the basics). Now there is something I can't understand: "800MHz FSB = DDR2 533MHz ( Ideal ) or DDR2 400MHz ( Matched but Slow. ) 1066MHz FSB = DDR2 667 ( Good ) or DDR2 533MHz ( Matched )".
If you have an Intel based platform with a FSB 800 CPU means that your basic FSB is 800 / 4 (Quad pumped) = 200. This means you should purchase the memory running at 200 * 2 = 400MHz. The article says to this combination "Matched but Slow". The 533MHz Ram has a basic freq. of 533 / 2 = 266MHz. How can this combination be IDEAL???.

I read in another article that running a FSB:RAM ratio of 1:1 is the best match but you will get better performance running the mem. 2 x FSB in an ratio of 1:2. In another words for an Intel based platform with a 800MHz FSB CPU the best combination would be buying 800MHz RAM (running the system in a 1:2 ratio).

I personally want to buy a 7xxx CPU with FSB 1066. To have a 1:1 ratio I would have to buy 1066 / 2 = 533MHz DDR2 modules (which run at a base freq. of 266MHz). But what if I buy DDR2@1066 MHz modules? According to the other articles I would run the system in a 1:2 ratio.

Now which is the best combination?